ISL68229IRAZ datasheet(24/107 Pages) RENESAS

24 / 107 page

ISL68229, ISL68239

4. Operating the Device

R16DS0006EU0101 Rev.1.01

Page 24 of 106

Jul 21, 2022

4.8

Diode Braking

Applications that support loads with large transient current demands often have significant output voltage

overshoot when the load current demand drops suddenly. In some cases, diode braking can allow overshoot

reduction at the expense of thermal dissipation in the low-side MOSFET.

4.9

Switching Frequency

Switching frequency is independently programmable on each rail from 200kHz to 2MHz.

4.10 Output Current Sensing

The ISL68229 and ISL68239 support DCR, resistor, and smart power stage current sensing. Use the differential

input CS and CSRTN pins to connect to the various sense elements.

4.10.1 SPS Current Sensing

In applications using Smart Power Stage (SPS), the SPS IMON output is connected to the corresponding

ISL68229 or ISL68239 CSn input. The CSRTNn pins are connected to the SPS current sense reference voltage.

For connection details, see Figure 1 on page 6 (ISL68229 typical application diagram) or Figure 2 on page 7

(ISL68239 typical application diagram).

4.10.2 Inductor DCR Sensing

Inductor windings have a resistive component (DCR) that drops a voltage proportional to the inductor current.

Figure 11 shows that the DCR is treated as a lumped element with one terminal inaccessible for measurement.

Fortunately, a simple R-C network as shown in Figure 11 can reproduce the hidden DCR voltage. By matching the

R-C time constant to the L divided by DCR time constant, it is possible to precisely recreate the DCR voltage

across the capacitor, so that VDCR(t) = VC(t), preserving even the switching frequency characteristic of the DCR

voltage.

Modern inductors often have such low DCR values that the resulting signal is <10mV. To avoid noise problems,

care must be taken in the Printed Circuit Board (PCB) layout to properly place the R-C components and route the

differential lines between controller and inductor. Figure 11 shows one PCB design method that places the R

component near the inductor VPHASE and the C component very close to the IC pins. The design method

maintains isolation of the noisy VPHASE node and maximizes filtering near the IC. Route the lines as a pair on a

single layer directly to the controller. Avoid routing the pair near any switching signals such as Phase and PWM.

This is the method used by Renesas on evaluation board designs. Note: The R component should be 0603 or

greater size to limit the effects of voltage coefficient of resistance in the resistor.

Because the DCR is actually the resistance of a metal winding, the DCR value increases with rising temperature.

The increase must be compensated or the sensed (and reported) current increases with temperature. To

compensate the temperature effect, the ISL68229 and ISL68239 provide temperature sensing options and an

internal methodology to apply the correction.

Figure 11. DCR Sensing Configuration

ISL68229IRAZ Datasheet(PDF) 24 Page - Renesas Technology Corp